Decibel value mentioned to tones (siggen package) not working as expected

[Foss User <fossist@gmail.com>]

I am using the tones command from siggen package.

$ rm notes.wav; tones -w notes.wav 1000 440@-2 0 440@-4 && play notes.wav

The command generates 3 tones, each one second long

1. 440 Hz at -2 dB
2. 0 Hz (silence)
3. 440 Hz at -4 dB

However, both the first and third tones sounds equally loud. From the
decibel values I have given, the first tone should have sounded louder
than the third. Can someone tell me what is going on?

N.B. The 'play' command is from sox package.